Hereditary persistence of fetal hemoglobin (HPFH) is a non-fatal condition in which adults produce fetal hemoglobin throughout adulthood. Because sickle cell anemia is ameliorated by the presence of fetal hemoglobin, HPFH is believed to be an identifiable modifier locus for other blood disorders such as sickle cell anemia and thalassemia. A series of families in Sardinia that display HPFH were previously genotyped with genetic markers from the candidate regions for the trait, chromosomes 6 and X. After linkage analysis, flanking markers for both candidate regions were genotyped and subsequent statistical analyses were performed, suggesting the need for additional genotyping in a larger sample.